Process and apparatus for making improved glass micro fibers

ABSTRACT

A process is provided for producing improved, superior and more cost effective glass micro fibers, wherein molten glass in filament form is attenuated into glass micro fibers by gasses of a combusted mixture of air and fuel. The improvement comprises introducing into the mixture a gas stream containing at east 70% by volume of oxygen. This avoids problems in glass micro fiber production where the quality of the fibers varies from time to time, as demonstrated by the quality of paper produced therefrom. An apparatus for producing the fibers is also provided, as well as improved glass micro fibers and improved papers made therefrom.

FIELD OF THE INVENTION

The present invention related to a process and apparatus for makingmicro fibers, and especially a process and apparatus that produces glassmicro fibers of uniform and improved quality, with greater costeffectiveness.

BACKGROUND OF THE INVENTION

In making glass micro fibers, typically high temperature burners combustfuel to reach temperatures for melting glass and attenuating extrudedstreams of molten glass into glass micro fibers. The velocity of thecombusted fuel gasses impinging on the streams of molten glass causesattenuation of the molten glass streams to produce the glass microfibers. Most of the velocity of the gas stream is a result of thethermal expansion of the combustion gases due to the rapid rise intemperature inside the burner or combustion chamber.

However, it is known that the quality of glass micro fibers varies fromtime to time, and that quality is most apparent in connection with theproperties of papers made with those glass micro fibers. While thisproblem with the glass micro fibers has long been recognized, the arthas not found either the reason for that variation in quality or a meansof avoiding that variation in quality. The present invention centersaround the discovery of the causes of that variation and a solution tothe problems engendered thereby. Accordingly, the present invention, inone aspect thereof, provides improved, superior fibers, as compared tothose of the prior art. In another aspect, the invention provides morecost effective fibers, as explained below.

In producing the glass micro fibers, ambient air and fuel, e.g.,petroleum fuel, especially natural gas, are drawn into a premixreservoir, gas train or directly into burners, or other combustiondevices, disposed in a combustion chamber/fiberizing zone and the fuelis combusted for melting, drawing and attenuating the molten glassstreams into glass micro fibers. It is important to the economics of theprocess that the amount of air (oxygen) is essentially stoichiometricwith the amount of fuel being combusted. If the amount of air (oxygen)is too little, incomplete combustion will result, normally referred toas operating in “rich” conditions. Then, as the combustion gases exitthe burner, any uncombusted fuel will combust with secondary air that isaspirated into the fiberization zone by the velocity of the flame. Thissecondary combustion has the effect of creating mini-explosions in thefiberizing zone, resulting in excessive turbulence that undesirablyshortens the length of fibers being formed. It is known that poor glassmicro fiber quality will result when operating in rich conditions.

On the other hand, if the amount of air (oxygen) is in excess,unnecessary amounts of nitrogen (from the air) must be heated to thecombustion temperature and expelled from the combustion chamber as partof the attenuating gas stream. This is normally referred to as operatingin “lean” conditions. If this extra heating doesn't occur, the velocityof the flame exiting the burner is reduced, limiting the ability of theflame/gasses to attenuate the glass streams into micro fibers. Torestore the necessary flame velocity, additional fuel/air mixture isnormally added to the combustion chamber. This is a considerable wasteof energy, and substantial excess air can make the combustion process,and hence the glass micro fibers, uneconomical. The present inventionavoids this difficulty, and, hence, provides a process that producesmore cost effective fibers.

Therefore, considerable effort is made in the art to induce into theburners or combustion chamber only a stoichiometric amount of air, orslight excess thereof, in order to ensure complete combustion, but nothave excess nitrogen (and other of the gasses of air) as a wasteby-product. This ensures a maximum throughput of glass and, hence,fibers, through the process. To this end, substantial instrumentation isused to ensure that the volume of air induced into the combustionchamber is substantially stoichiometric with the amount of fuel fed tothe chamber, either directly or through a premix gas train or reservoir.

However, as noted above, it is known that the quality of the glass microfibers that results from this process varies from time-to-time, asexhibited by the properties of paper produced from those glass microfibers.

BRIEF DESCRIPTION OF THE INVENTION

The invention is based on several primary discoveries and severalsubsidiary discoveries.

First, it was found that the quality of the glass micro fibersdeteriorated with the seasonal variations of the ambient air inductedinto the combustion burners. Stated another way, in more practicalterms, it was found that, in general, the micro fibers produced duringthe winter months were superior to the glass micro fibers producedduring the summer months, in terms of the quality of paper that could beproduced from the respective micro glass fibers. This was completelyunexpected.

Second, of the variables involved in the seasonal variations of ambientair, it was found that the variable most responsible for thedeterioration of the quality of the glass micro fibers is the moisturecontent of the ambient air. Typically, in the summer, the relativehumidity of ambient air will be greater than in winter and a standardvolume of air will have increased amounts of water. In certain regionsthe seasonal range of indoor relative humidity can be extreme. Insidethe manufacturing plants, winter air, brought into the plant and heated,can be extremely dry, with relative humidity levels approaching zero. Inthe summer, relative humidity levels can approach 100%.

Like nitrogen, mentioned above, it was found that the humidity/wateracts as a diluent, cooling the combustion process, and thus eitherincreasing fuel requirements or reducing the efficiency of thefiberization process. Most importantly, and unlike nitrogen, it wasrecognized that water vapor is also a combustion product, and accordingto Le Chatelier's Principle, increasing its concentration in thecombustion zone will force the combustion reaction away fromequilibrium, or in this case, away from complete combustion. This is amost important discovery. Therefore, in highly humid conditions, theglass micro fiber production process will act like it is operating rich,even if the air/fuel ratio is perfectly adjusted. Resulting poor qualityglass micro fibers will, and do occur.

It was found that the only way to bring the equilibrium back in balanceis to increase the concentration of the non-fuel reactant, i.e., oxygen.Increasing the concentration of fuel is not a solution, since it wouldmake the combustion conditions even richer. Increasing the reactants,i.e., fuel and air, stoichiometrically, would not shift the equilibriumbecause of the Le Chatelier's Principle. Consequently, to achievecomplete combustion in highly humid conditions, only the addition ofadditional oxygen, not just air, will avoid the problem of a shift ofequilibrium because of the Le Chateliers's Principle.

Thus, as further discovery, it was found that simply increasing thevolume of air in the summer to compensate for the high humidity is notan effective approach to solving the problem. In addition to the abovereason, increased volumes of air also introduces into the combustionprocess increased volumes of water vapor (thus increasing the problemnoted above) and nitrogen, both of which must be heated to thecombustion temperature during combustion and expelled from the processas waste stack gasses. The resulting energy loss by simply increasingthe volume of ambient air introduced into the combustion process is toogreat and renders the resulting process uneconomical.

As a result of the above discoveries, it was found that substantiallypure oxygen could be introduced into the process. This avoids theequilibrium shift, discussed above, and energy loss by increasednitrogen and water vapor induced by additional ambient air but, at thesame time, increases the oxygen content of the air to effect completecombustion. By this technique, combustion efficiencies rise, the propertemperature for uniform attenuation (fiberization) is reached, andexcess heat loss is avoided in expelling excessive amounts of wastenitrogen and water vapor. Also, this maximizes the through-put of glassand, hence fibers, in the process, which increases the costeffectiveness of the process.

It was further found that with today's technology, oxygen could begenerated at the site of a combustion chamber in a most economicalmanner and fed directly into the process. This makes control andoperation of the process quite easy and economical.

Further, this approach avoids the result of a “starving” amount ofoxygen in the combustion mixture during the summer when additionalambient air is introduced into the combustion process, which results inexcess and uncombusted fuel combusting downstream of the combustionchamber and the attenuation zone of the fiberizer, which causes anfurther unstable attenuation of the glass streams, as described above.The unstable attenuation can result in shortened and unwanted fibers,which, again, is apparent from the deteriorated paper produced from suchfibers.

Thus, in summary, the present invention provides a process for producingimproved and more cost effective glass micro fibers, wherein moltenglass in filament form is attenuated into glass micro fibers by gassesof a combusted mixture of air and fuel, the improvement comprisingintroducing into the mixture a gas steam containing at least 70% oxygen.Correspondingly improved fibers and papers made therefrom are alsoprovided.

The present invention also provides a fiberizer apparatus for producingimproved, superior and more cost effective glass micro fibers comprisinga premix device for combining ambient air flowing from an ambient airinlet and fuel flowing from a fuel inlet, an oxygen analyzer foranalyzing an oxygen content of the combined air and fuel in the premixdevice, an oxygen generator for generating oxygen and flowing thegenerated oxygen to the premix device, a controller for adjusting theflow of oxygen from the oxygen generator to the premix device inresponse to signals generated by the oxygen analyzer so as to providedthe mixture with at least 22% by volume of oxygen, and a burner forcombusting the mixture into a flame in a former tube device for drawingand attenuating primary filaments of molten glass into glass microfibers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of a form of the apparatus forcarrying out the process of the invention.

FIG. 2 is a diagrammatic illustration of a preferred form of a spargerarrangement for injecting oxygen into the process.

DETAILED DESCRIPTION OF THE INVENTION

The invention involves enriching ambient combustion air, or ambient airin an ambient air/fuel mixture, for use in a combustion process forfiberizing molten glass streams into glass micro fibers, to between 22and 35 volumetric % oxygen, by adding substantially pure oxygen, e.g.,at least 70% pure oxygen, to the air or air/fuel mixture. Thatintroduction is, preferably by way of the special spargers, describedmore fully below, or other means. The important point is theintroduction of the substantially pure oxygen into the combustionprocess to avoid production of inferior micro fibers, as describedabove, and, thus, provide improved, superior and more cost effectivefibers.

The oxygen may be obtained from any desired source, but commerciallyavailable “packaged” systems are preferred, e.g., PSA (Pressure SwingAdsorption) or VSA (Vacuum Swing Adsorption) systems. This is becausethey may be placed near a conventional combustion chamber/fiberizerapparatus and easily generate the required amounts of oxygen insufficient purity. For example, OGS Company has available multi-tonoxygen generators with outputs of from 1250 to 5000 SCFH capacities. Theunits are available with telemetric communication packages so that theycan easily be controlled to provide the required amount of oxygen atvariable rates in response to process needs. Depending on ambientconditions like relative humidity and temperature, the oxygen generator,through storage tanks, will supply oxygen so that the incoming air tothe combustion process is at least 22% by volume and up to 35% by volumeoxygen.

The overall process is shown in Fig. 1. As shown in that Figure, glassis melted in melting pot 1 and extruded from bushing 2 through aplurality of spinnerets 3 into a series of primary filaments 4. Theprimary filaments are gathered by pull rolls 5 and 6 into guide rolls 7and 8 of fiber guide 9.

A burner 10 is fed by pipe 11 with a fuel/air mixture from conventionalgas train or premix device 12, which mixes(combines) ambient air fromambient air inlet 13 and fuel from fuel inlet 14. Oxygen analyzer 15analyzes the oxygen content in the gas train or premix device 12 andsends signals to controller 16 through line 17. The controller 16, inturn, sends signals through line 17 a to adjust the flow of oxygenthrough pipe 18 from control valve 19 of a “package” oxygen generator20.

The burner 10 combusts the air/oxygen/fuel mixture from pipe 11 into aflame in former tube device 21 where the flame draws and attenuates theprimary filaments 4 into fibers 22 (the fiberizer unit) . Optionally, aconventional binder material may be sprayed onto the fibers by bindersprays 23. The burner 10 shown in the figure is shown as a genericburner, but it is preferred that the burner be a slot burner asdescribed in U.S. Pat. No. 2,569,699. That patent also describes thedetails of the process summarized above, and the disclosure of thatpatent is incorporated herein by reference for those details.

The fuel used in the process may be any gaseous, oxidiziable fuel, buthydrocarbon fuel, e.g., natural gas, liquefied petroleum gas, et cetera,is preferred for obvious reasons. The oxygen may be pure oxygen, butsomewhat impure oxygen, such as that produced by the “package” units,described above, is preferred due to the economics. The oxygen, however,should be substantially pure oxygen, e.g., the oxygen stream shouldconsist essentially of oxygen, and especially the oxygen stream shouldbe at least 70%, e.g., 75% and especially 85% oxygen. This avoidsuneconomical amounts of waste gases being heated to the fiberizingtemperatures, for the reasons explained above. However, pure oxygen isquite expensive and less than pure oxygen, as identified above, ispreferred.

Of course, care should be exercised when introducing oxygen into afuel/air mixture, and to that end, it is preferred that the oxygen beintroduced into the mixture by way of special spargers. One establishedway of such introduction is that of introducing the oxygen into the airstream prior to introducing the resulting oxygen/air mixture into thefuel. Special spargers are available for introducing oxygen into an airstream and one sparger that is preferred is that made by AIR LIQUID, anddesignated as the OXYNATOR TM. These devices are of the type known asthe swirl-type sparger, which introduces the oxygen at the center of anair pipe and imparts spin in order for mixing of the oxygen and air tooccur. This avoids high oxygen concentrations near the pipe wall andavoids a possible danger.

FIG. 2 diagrammatically illustrates the foregoing arrangement. As shownin that Figure, air flowing in air inlet pipe 13 is mixed in sparger 25with oxygen flowing in oxygen inlet pipe 18. The mixture is then pastedthrough inlet pipe 13, again to gas train or premix device 12, as shownin FIG. 1.

By using the oxygen enhanced process in such a way as to make superiorquality fiber, as described above, hand sheets made of fibers from thatprocess have at least a 16% better tensile strength, g/in., and about atleast a 28% increase in double fold tensile strength, g/in. This lattertensile is particularly important since it more relates to necessaryproperties for pleated (folded) filters. This shows that the presentprocess provides substantially improved and superior fibers and papersproduced therefrom. However, the use of the oxygen enhanced processcould also be optimized to make a less costly product with qualitysimilar to standard glass fibers by taking advantage of the thermalefficiencies offered by the hotter, higher velocity enriched flame.Further, since the present process avoids both the “lean” and “rich”conditions of the prior art, as explained above, the problems, includingthe economic problems thereof, are avoided and, thus, the presentinvention provides more cost effective fibers.

Of course, the process of the invention could be used for making microfibers from materials other that glass, e.g., inorganic fiber formingmaterials such as various metals and organic fiber forming materialssuch as thermoplastic polymers, but it is especially useful forproducing glass micro fibers, as fully described above.

1. In a process for producing improved, superior and more cost effectiveglass micro fibers, wherein molten glass in filament form is attenuatedinto glass micro fibers by gasses of a combusted mixture of air andfuel, the improvement comprising introducing into the mixture a gasstream containing at least 70% by volume of oxygen.
 2. The process ofclam 1, wherein the gas stream contains at least 75% oxygen.
 3. Theprocess of claim 2, wherein the percentage of oxygen is at least 85%. 4.The process of claim 3, wherein the gas stream consists essentially ofoxygen.
 5. The process of claim 4, wherein the gas stream consists ofoxygen.
 6. The process of claim 1, wherein the oxygen stream is producedby a packaged oxygen generator.
 7. The process of claim 1, wherein theoxygen is introduced into an air stream, which air stream is in turnintroduced into the fuel by a sparger.
 8. The process of claim 7,wherein the sparger is a swirl-type sparger.
 9. The process of claim 1,wherein after introduction of the gas stream containing the oxygen intothe mixture, the mixture is between 22 and 35% by volume oxygen.
 10. Afiberizer apparatus for producing improved, superior and more costeffective glass micro fibers, comprising: (1) a premix device (12) forcombining ambient air flowing from an ambient air inlet (13) and fuelflowing from a fuel inlet (14); (2) an oxygen analyzer (15) foranalyzing an oxygen content of the combined air and fuel in premixdevice (12); (3) an oxygen generator (20) for generating oxygen andflowing the generated oxygen to the premix device (12) to form a mixtureof oxygen/air/fuel; (4) a controller(16) for adjusting the flow ofoxygen from generator(20) to the premix device(12) in response tosignals generated by oxygen analyzer(15) so as to provide the mixturewith at least 22% by volume oxygen; and (5) a burner (10) for combustingthe mixture into a flame in a former tube device (21) for drawing andattenuating primary filaments (4) of molten glass into glass microfibers (22).
 11. The apparatus of claim 10, wherein the flow of oxygenfrom generator (20) is introduced into the ambient air flowing intopremix device (12).
 12. The apparatus of claim 11, wherein the flow ofoxygen is introduced into the ambient air by a sparger (25).
 13. Theapparatus of claim 12, wherein the sparger is a swirl-type sparger. 14.The apparatus of claim 10, wherein the oxygen generator is a packagedoxygen generator.
 15. The apparatus of claim 14, wherein the packagedoxygen generator is near the fiberizer apparatus.
 16. Improved glassmicro fibers which can be formed into a paper with at least a 16% bettertensile strength.
 17. The fibers of claim 16, which can be formed into apaper with at least a 28% increased double fold tensile strength.
 18. Apaper made of the fibers of claim
 16. 19. A paper made of the fibers ofclaim 17.